Slope failure hazard in Canada’s Atlantic Provinces: a review Ian Spooner1*, Martin Batterson2, Norm Catto3, David Liverman2, Bruce E. Broster4, Kim Kearns5, Fenton Isenor6, and G. Wayne McAskill7 1. Department of Earth and Environmental Science, Acadia University, Wolfville, Nova Scotia B0P 1X0, Canada 2. Geological Survey of Newfoundland and Labrador, Department of Natural Resources, Government of Newfoundland and Labrador, PO Box 8700, St. John’s, Newfoundland and Labrador A1B 4J6, Canada 3. Department of Geography, Memorial University of Newfoundland, St. John’s, Newfoundland and Labrador A1B 3X9, Canada 4. Department of Earth Sciences, University of New Brunswick, Fredericton, New Brunswick E3B 5A3, Canada 5. ESRI, 380 New York St., Redlands, California 92373-8188, USA 6. Cape Breton University, P.O. Box 5300, 1250 Grand Lake Road, Sydney, Nova Scotia B1P 6L2, Canada 7. Nova Scotia Department of Transportation and Public Works, 107 Guysborough Road, Fall River, Nova Scotia B2T 1J6, Canada *Corresponding author <[email protected]> Date received 26 February 2012 ¶ Date accepted 30 November 2012 ABSTRacT Slope failures present a hazard around the world, with considerable impact on communication/ transportation corridors, resource sectors, and coastal and urban development. Although poorly documented in much of Atlantic Canada, mass movements are known to have resulted in 71 fatalities in Newfoundland. In the Ferryland, Newfoundland, disaster of around 1823, 42 fishermen were reportedly killed when a cave roof collapsed onto them. Debris floods and flows are widespread in areas of higher relief in both Newfoundland and Cape Breton Island, and tend to be most hazardous for highway engineering and community development. Rotational slumps in glaciomarine clays are evident along the major river valleys of Labrador and are an important consideration during hydroelectric development. In other areas of Atlantic Canada, earthflows affect transportation routes and involve movement of saturated sediment during spring thaw. Along the Gulf of St. Lawrence, Northumberland Strait and the Bay of Fundy coastlines, friable rocks, glaciotectonic activity, frost wedging, and coastal erosion have resulted in many small failures and incremental retreat of coastal cliffs. Ongoing climate change will have an impact on slope failure activity. Increasing summer frequency and intensity of thunderstorms and hurricane events, increased winter precipitation in some locations, and possible erratic freeze-thaw events would result in an increase in debris flows triggered by precipitation, and rockfalls triggered by freeze-thaw. Human utilization of coastal areas is also contributing to the frequency and hazard of slope failures across Atlantic Canada. RÉSUMÉ Les ruptures de versant représentent un danger partout dans le monde et ont une incidence considérable sur les corridors de communication ou de transport, les secteurs des ressources et l’aménagement côtier et urbain. Bien qu’ils soient mal documentés dans une bonne partie du Canada atlantique, ces mouvements de masse sont réputés pour avoir causé 71 décès à Terre-Neuve. Dans la catastrophe de Ferryland, à Terre-Neuve, ATLANTIC GEOLOGY 49, 1- 14 (2013) doi: 10.4138/atlgeol.2013.001 Copyright © Atlantic Geology 2013 0843-5561|14|00001-14 $3.25|0 Atlantic Geology . Volume 49 . 2013 2 vers 1823, 42 pêcheurs auraient été tués lorsque le plafond d’une caverne s’est effondré sur eux. Les inondations et coulées de débris sont courantes dans les zones de relief élevé à Terre-Neuve et à l’île du Cap-Breton, et elles tendent à être très dangereuses pour la conception des routes et le développement des localités. Des glissements rotationnels dans les argiles glaciomarins sont manifestes le long des vallées fluviales importantes du Labrador et sont un facteur important à considérer lors d’aménagements hydroélectriques. Dans d’autres régions du Canada atlantique, les coulées de terre perturbent les routes de transport et entraînent le mouvement de sédiments saturés durant le dégel printanier. Le long des côtes du golfe du Saint-Laurent, du détroit de Northumberland et de la baie de Fundy, des roches friables, de l’activité glaciotectonique, de la gélifraction et de l’érosion côtière ont donné lieu à de nombreuses petites ruptures et au recul graduel des falaises côtières. Les changements climatiques en cours auront une incidence sur les ruptures de versant. La fréquence et l’intensité accrues des orages et des ouragans pendant l’été, l’augmentation des précipitations hivernales dans certains endroits et la possibilité de gels-dégels erratiques pourraient se traduire par une augmentation des coulées de débris déclenchées par les précipitations et des éboulements déclenchés par les gels-dégels. L’utilisation humaine des zones côtières contribue également à la fréquence et à la dangerosité des ruptures de versant dans l’ensemble du Canada atlantique. [Traduit par la redaction] INTRODUCTION SLOPE FAILURE IN NEWFOUNDLAND AND LABRADOR Some authors consider landslides not to be a major hazard in Atlantic Canada (Cruden et al. 1989; Evans 2001). A variety of slope failure types has occurred in In a compilation of Canadian landslide disasters, Evans Newfoundland and Labrador, including sackung; rockfalls; (2001), who defined a disaster as “an incident with three or debris torrents and floods; channelized debris flows and more fatalities”, showed that only one such event out of 45 debris avalanches; rotational slumps; and gelifluction occurred in the region. However, it is misleading to assume creep. Many incidents have been documented, with over that landslides are insignificant in the area and inappropriate 80 having been recorded as impacting communities and not to recognize potential risks to life and property (Fig. 1). infrastructure (Batterson et al. 2006). Some have been fatal, Liverman et al. (2001) and Batterson et al. (2006) reviewed including two landslides in St. John’s (1936 and 1948) and geological hazards in Newfoundland and tabulated known the 1973 Harbour Breton landslide that killed four children. landslides there. Additional research, documented here, Landslides involving rotational slumping of large masses of indicates that 29 to 71 fatalities in Newfoundland alone sediment have been recorded on the west coast of the island, may have occurred from landslides, as well as 68 from including events at Port au Port East in 1994; near Journois, snow avalanches (Liverman et al. 2001, 2003; Batterson St. George’s Bay in 1996; at Daniel’s Harbour in 2007–2008; et al. 2006). In Nova Scotia, five fatalities associated with and at Trout River in 2009 (Fig. 1). The last two examples snow avalanches have been documented (Isenor et al. 2005; caused no loss of life, but resulted in considerable property Spooner et al. 2010). damage and the relocation of several residences. Other slope Our objective is to summarize the variety of slope failures have occurred in remote areas, where they have had failure processes that are active in Atlantic Canada, with little impact on society, but may need to be considered if examples of recent and/or significant events. We also provide development takes place in the future. an overview of slope failure research in the region and indicate where further study is warranted. We demonstrate that slope failures are common and have a significant Sackungen impact on communication/transportation corridors, the resource sector, coastal and urban development, and other A “sackung” (plural sackungen) is a deep-rooted, activities. We use the terms slope failure and mass wasting generally slow-moving slope failure involving large volumes interchangeably to describe the downslope movement of of bedrock. A sackung is identified on aerial photographs rock debris and soil in response to gravitational stresses. We by a series of linear scarps that face up-slope; these are use the term landslide when the responsible mechanisms called “anti-slope scarps”. Grant (1974, 1987) identified 24 and the velocity of movement allow the slope failure to examples, mostly developed in ultramafic rocks in western be classified in detail. This review is restricted to onshore Newfoundland. The slowness of motion, combined with impacts, although the offshore is equally prone to slope the absence of residential or commercial development in movements. We review slope failures province-by-province, areas where these occur, limit their significance as a hazard. emphasizing the characteristic slope failure styles for each In times of exceptional rainfall, movement may accelerate (Fig. 1). We do not include snow avalanche hazards in this (Evans and Clague 2003), and a rapid collapse into water review. might generate displacement waves. Slope failure hazard in the Atlantic Provinces: a review Copyright © Atlantic Geology 2013 Atlantic Geology . Volume 49 . 2013 3 Figure 1. Location of selected slope failure sites discussed in detail in the text. CBI = Cape Breton Island, NB = New Brunswick, NL = Newfoundland and Labrador, NS = Nova Scotia, PEI = Prince Edward Island, P.P. = Provincial Park. The largest example of a sackung in Newfoundland is Bay. Although the failure was initiated post-glacially, at Norris Point in Bonne Bay (Figs. 1, 2), where a rock mass a more precise age of failure has not been determined. estimated at 10 km3 has moved vertically by approximately Visual examination from 1974 to 2003 suggested that no 100 m (Fig. 2; Grant 1974). The head of the failure consists discernable movement was occurring during